1. Field of the Invention
The present invention relates to a resin coated piston manufacturing apparatus for a shock absorber in which a resin sheet such as a tetrafluoroethylene resin or the like is adhered to an outer periphery of a piston raw material, in order to improve a sealing performance, an abrasion resistance and a sliding performance of a piston used in a hydraulic shock absorber for a motor vehicle or the like.
2. Description of the Related Art
Japanese Patent No. 3400080 (patent document 1) discloses a structure which aims to manufacture a resin coated piston for a shock absorber having a good quality by securely adhering a resin sheet made of a thin and soft raw material to a piston raw material without damage.
The prior art is structured such that in a resin coated piston manufacturing apparatus for a shock absorber in which a washer-shaped resin sheet is adhered to an outer periphery of a cylindrical piston raw material having a plurality of annular grooves in an outer periphery, there is provided: a set mold in which a resin sheet set hole is open to an upper end portion, a means for setting the resin sheet within the resin sheet set hole of the set mold, a means for aligning and setting a cylindrical piston raw material on the resin sheet set to the set mold, a means for pressing the cylindrical piston raw material to the resin sheet until the resin sheet is locked to a resin sheet locking annular groove of the cylindrical piston raw material, and continuously arranged heating and cooling cylinders having reciprocating ram pressing the piston raw material to which the resin sheet is locked, wherein the resin sheet set hole open to the upper end portion of the set mold has an inner diameter which is slightly larger than an outer diameter of the washer-shaped resin sheet to be adhered, a concave portion having a larger inner diameter than an outer diameter of the piston raw material is formed in a lower side of the resin sheet set hole via a step portion, the step portion has a curved surface having a radius R of curvature, and an aligning guide to which an inner diameter of the piston raw material is capable of being fitted from a center of a lower concave portion is provided so as to extend to a center axis of the set mold.
Further, the prior art is structured such as to be provided with an injection jet holding a laminated body of the washer-shaped resin sheets having a center hole so as to move up and down along a vertical holding rod inserted to the center hole, and separating the top end resin from the resin sheet in a lower side thereof by injecting a gas in a tangential direction near the top portion of the laminated body, and a pressure reduction suction device adsorbing and holding the sheet in the top stage so as to set within the resin set hole of the set mold from the laminated body.
Further, in this prior art, the heating cylinder has an inlet end inner diameter D which is smaller than a dimension obtained by adding twice the thickness of the resin sheet to all outer diameter of the piston raw material, and an inner diameter E which is smaller than the inlet end inner diameter D from the inlet end via a taper portion. The cooling cylinder has an inner diameter equal to or less than the inner diameter of the heating cylinder, and is provided with a reciprocating plusher pressing the piston raw material to an upper end inlet of the heating cylinder from a resin sheet locking end portion so as to push forward at a predetermined press pitch.
Further, in this prior art, the structure is made such that a plurality of the set molds are provided on a turn table at spaced positions in a circumferential direction, the resin sheet set apparatus, the piston raw material set apparatus, the resin sheet locking apparatus and the heating and cooling cylinder apparatus are arranged around the turn table, and a control apparatus is provided in such a manner as to synchronously actuate the turn table, the resin sheet set apparatus, the piston raw material set apparatus, the resin sheet locking apparatus and the heating and cooling cylinder apparatus.
The prior art has the following problems.
(1) Since the cylindrical piston raw material is set on the resin sheet set to the set mold, it is necessary to be provided with the means for aligning and setting the piston raw material on the resin sheet, specifically, the aligning guide to which the inner diameter of the piston raw material can be fitted from the center of the lower concave portion of the set mold in an extending manner.
It is necessary to execute the operation of fitting the inner diameter of the piston raw material to the aligning guide during setting of the piston raw material into the set mold, complicating the piston raw material set apparatus.
(2) Since the cylindrical piston raw material is set on the resin sheet set to the set mold, it is impossible to simultaneously execute a step of setting the resin sheet to the set mold, and a step of setting the piston raw material to the set mold, extending the manufacturing time.
(3) Since the means (the pressing cylinder apparatus) for pressing the piston raw material to the resin sheet until the resin sheet is locked to the resin sheet locking annular groove of the piston raw material is separately formed from the reciprocating ram (the press cylinder apparatus) pressing the piston raw material to which the resin sheet is locked, two cylinder apparatuses are necessary, and the structure becomes complicated.
(4) Since the means (the pressing cylinder apparatus) for pressing the piston raw material to the resin sheet until the resin sheet is locked to the resin sheet locking annular groove of the piston raw material is separately formed from the reciprocating ram (the press cylinder apparatus) pressing the piston raw material to which the resin sheet is locked, the step of pressing the piston raw material by the pressing cylinder apparatus is discontinuous from the step of pressing the piston raw material by the press cylinder apparatus, and the manufacturing time becomes elongated.
(5) The structure is made such that the means for setting the resin sheet to the resin sheet set hole of the set mold is provided with the injection jet injecting the gas in the tangential direction near the top end portion of the laminated body of the resin sheet so as to separate the resin sheet in the top end from the resin sheet in the lower side thereof and the pressure reduction suction device adsorbing and holding the sheet in the top stage so as to set within the resin sheet set hole of the set mold from the laminated body. It is necessary to adjust an injection pressure of the injection jet, and it is hard to always accurately and stably separate only one resin sheet. Since the pressure reduction suction device is used, a pressure reduction generating means such as a vacuum pump or the like is necessary.
(6) Since the inner diameter of the cooling cylinder is made equal to or less than the inner diameter of the heating cylinder, the resin sheet adhered to the piston raw material is caught on a boundary between the heating cylinder and the cooling cylinder during pressing of the piston raw material. Because the resin sheet is locked to the cooling cylinder via the heating cylinder, it is impossible to smoothly press, and there is a risk that the resin sheet hot formed within the heating cylinder is damaged.
(7) Since the resin sheet set apparatus, the piston raw material set apparatus, the resin sheet locking apparatus and the heating and cooling cylinder apparatus are arranged around the turn table, and the respective apparatuses are synchronously actuated, the number of the steps is totally four, extending the manufacturing time, and the manufacturing apparatus is enlarged in size.